1. Field of the Invention
The present invention relates to a semiconductor optical device and a method of making the same.
2. Related Background Art
Document 1 (Japanese Patent Application Laid-Open No. 5-3362) describes a semiconductor optical device having a ridge type waveguide structure. In this ridge type semiconductor optical device, a contact layer is formed on the ridge. An insulating layer covering the ridge and contact layer has an aperture (window) at which a portion of the contact layer is exposed. The aperture is formed, for example, by photolithography using a photomask. However, if the alignment of the photomask is inaccurate, the aperture is not formed at a desired position. Further, the use of the photomask complicates a process of fabricating the semiconductor optical device and increases production cost.
Document 2 (Japanese Patent Application Laid-Open No. 08-078784) and Document 3 (Japanese Patent Application Laid-Open No. 09-331104) describe that an insulating layer on the contact layer has an aperture formed by a self-alignment method without using the above mask alignment and that the contact layer is exposed at the aperture. The self-alignment method is free of misalignment because of no need for the alignment of the mask. In the self-alignment method, the insulating film is formed on a substrate and a photoresist film is formed onto the insulating film. Since the thickness of the photoresist film becomes smaller on the ridge, the photoresist film on the ridge can be selectively removed.